Filter protection



April 11, 1939. w, w RTENI 2,154,051

FILTER PROTECTION Filed Jan. 24, 1938 INVENTOR "VilliounW MarienisATTORNEY Patented Apr. 11, 1939 PATENT OFFICE FILTER PROTECTION WilliamW. Martenis,

Minneapolis, Minn, as-

signor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn.,

( Delaware a corporation of Application January 24, 1938, Serial No.186,565

15 Claims.

The present invention relates generally to warm air heating systems andpertains more particularly to the elimination of the fire hazardattendant to the use of combustible air filters in such'systems.

In present warm air heating systems, it is customary to employ a fan forenforcing air circulation thus making possible the use of air filtersfor the purpose of removing foreign matter which may otherwisecontaminate the air stream. It is quite general also to employ aneconomizerwhich is a tortuous passage-way through which the gases ofcombustion pass on the way to the stack or flue. The "economizer isarranged in heat. exchangerelation with the return air so as to preheatit. As the trend in modern furnace design is toward placing all theelements associated with the furnace in as small a casing as possible inthe interests of compactness and economy of space it is usual that thefilters and economizer are located in close proximity in the return airsection of the furnace. The economizer temperature is rather high andparticularly at times when the forced air circulation occasioned by thefurnace fan fails there is grave danger of igniting the filters whichordinarily are made of combustion material. The fire hazard isespecially serious when the return air ducts are formed between woodenjoists and flooring of frame buildings. Furnace fan failure may occur asa result of the fan belts breaking or failure of power to the drivingmotor. From experience it has. been found that upon fan failure theeconomizer temperature quickly rises to a temperature 35 at whichignition of the filter material may take place. Failure of power for thefan motor is decidedly serious injthe case of coal fired hot airfurnaces inasmuch as the fire continues after the fan stops and theeconomizer temperature quickly rises to the danger point.

It is the above described serious fire hazard attendant to the use offilters in furnace fan warm air heating systems which it is the primaryobjective of my invention to overcome.

Among other objects of my invention is to provide positive means forisolating the filters from the furnace in a warm air heating systemwhenever the forced air circulation occasioned by the furnace fan fails.

Another object is to provide a damper closin device in the return airchamber between the filters and the furnace in the above describedsystem, the damper device to be held open only when forced circulationis" being provided by the 55 fan. Concurrently with this object it is afurther object to provide a power failure motor for operating the damperdevice arranged to cause closing of the damper device whenever the motoris deenergized.

It is another object of-the invention to control the power failure motorreferred to in the previous object from a sailswitch located in the pathof the enforced air circulation.

Other objects and purposes of the invention will become apparent from anexamination of the drawing and the more detailed description following.

The single figure of the drawings represents somewhat diagrammatically awarm air heating system having my invention incorporated therein.

- Referring to the drawing, numeral i0 represents generally a furnacecasing forming part of a warm air heating system having conduits ii andI2 for conveying air to and from the casing of the furnace respectively.The conduits i2 and Il may have branch conduits l3 and id as shown forconveying air to and from various rooms of a building as shown. Thefurnace casing in is divided into three separate compartments orchambers designated l6, l1, and I8. The chamber l6 houses anelectrically driven oil burner i9 of conventional type and locatedwithin the chamber i1 is a furnace or combustion chamber proper 20 whichserves to heat the air within the chamber H. The nozzle of the oilburner 19 extends from the chamber I6 through the chamber ii and intothe combustion chamber 20. The oil burner l9 has electrical terminals 22and 23 which connect to electrical conductors for supplying power to theoil burner. Within the combustion chamber 20 and adjacent the end of thenozzle of the oil burner is located a pipe 2| communicating with asupply of gas whereby a pilot flame 25 may be kept constantly burningfor igniting the fuel from the oil burner whenever the burner is to beput into operation. Located adjacent to the pilot flame 25 so as to beheatedthereby is a bimetallic thermostatic element 25 forming withcontact 21 an electrical switch serving as a safety device to shut oilthe oil burner whenever the pilot flame should become accidentlyextinguished. The control instruments and wiring of the apparatus willbe presently described.

The chamber l8 of the furnace casing forms a return air chamber throughwhich the cooler air from the spaces being heated is passed before beingforced over the furnace or heating chamber in the path of the return airchamber l8. Heat from the burnt gases of combustion is therefore given011 to the return air and serves to preheat the return air on itspassage through the furnace casing. The end of the tortuous passage-wayin the economizer 2| communicates with a pipe 30 which serves to conveythe burnt gases of combustion to av conventional stack or flue. Thereturn air chamber I8 of the furnace casing includes a portion 3| withinwhich are located filters 32 for removing impurities such as dirt anddust with which the air may have become contaminated in the spaces beingheated. The filters comprise slabs of any suitable material which willfilter out or remove impurities from the air without substantiallyobstructing the passage of air therethrough. The slabs 32 of filtermaterial are supported between supporting members 33 and the walls ofportion 3| of the furnace casing. It will be noted that portion 3| hasan internal dividing wall 34 which divides it into two portions, theupper end of one of the slabs 32 resting against this internal dividingwall. By reason of the arrangement of the filters they may be removed atwill from the furnace casing and replaced by new ones whenever they havebecome unduly fouled with foreign matter from the stream of air passedthereover. The return air from the spaces being heated is conveyedthrough conduit through the portion 3| of the return air chamber andpast the economizer 2| to be preheated on its way through the return airchamber. At the lower part of the return air chamber is a fan or blower36 which draws in air from the return air chamber and forces it througha conduit 31 through the air heating chamber I! to conduit 2 and therebyproviding a forced circulation of air in the entire system. The fan 36is of conventional type and is driven by an electric motor 31 through abelt 38 or other similar drive means.

Positioned so as to be affected by the circulation of the air in thedischarge conduit 31 of the fan is a member pivoted at 39 having amercury switch 4| located at the upper end thereof. The elements 40 and4| form a sailswitch which is closed whenever the enforced circulationof air in the discharge conduit 31 causes the lower part of the member40 to be moved to the left so that the mercury in the switch 4| engagesthe electrodes therein.

Positioned between the filter members 32 and the economizer 2| in thereturn air chamber l8 are a plurality of louvre members forming a damperfor closing off the circulation of air which normally passes over thefilter members and thence over the economizer. The louvre members 45 arepivotally connected to an operating link 46 so as to be moved in theconventional manner in which dampers are operated. The link 46 isconnected by another link 41 to a rack 48 driven by a pinion 49. Thepinion 49 is driven by a shaft 50 connected to an electrical dampermotor 5| which may be of a conventional type. The damper motor 5| haselectrical terminals 53 and 54 for connecting to electrical conductorsfor supplying power to the damper motor. The damper operating link 46has pivoted thereto a lever 56 the opposite end of which is pivoted to alink 51 which is connected to' a coil spring 58 which causes the lever56 to be biased in a clockwise direction. When the link member 46 hasbeen moved to the right sufficiently to position the louvre members 45vertically the lever 56 engages a suitablestop member 60. In normaloperation the damper motor 5| is energized and through pinion gear 49and rack 48 retains the link 46 in its extreme right-hand position withthe lever 56 engaging stop 60 and the louvres in vertical position. Inthis position the spring 58 is under tension and should motor 5| becomedeenergized the spring will move lever' 56 in a clockwise direction andclose the dampers by moving the louvres 45 into a horizontal position.

The heating system is primarily controlled by a thermostat generallyindicated at 63 which may be located in one of the rooms being heated.The thermostat is of conventional type comprising a circularly arrangedbimetallic element 64 connected to a movable arm 65 having a switchcontact 66. The switch contact 66 is arranged to make or break anelectrical circuit through a fixed contact 61. The system isadditionally controlled by mercury switches 68 and 69 which are operatedby a thermostatic element 10 of the helical type arranged to beresponsive to the temperature of air being heated within the chamber IT.The thermostatic element 10 is adjusted so as to cause switch 69 toclose the circuit therethrough at a predetermined temperature within thechamber Switch 68 is normally closed and is opened by element 10 at apredetermined relatively high temperature. 1

Referring to the electrical wiring connecting the various devicesincluded in the system and the instruments for controlling them,numerals I2 and 13 indicate line conductors connected to an externalsource of power (not shown). The line conductor 13 is connected by awire 14 to the motor 31 for driving the fan 36. The circuit to the motor31 is completed by wire 15 which connects the motor to the switch 69 andthe wire 16 which connects switch 69 to the line conductor 12. It willbe seen therefore that whenever the thermostatic element 10 causesswitch 69 to close, motor 31 operating the fan will be put intooperation enforcing the circulation of air through the system.

The electrical circuit for providing power for the oil burner I9 issupplied through a wire 80 connected to the wire 14, a wire 8| whichconnects the oil burner to the thermostatic switch 26, a wire82'connecting the thermostatic switch to the mercury switch 68, a wire83 connecting the mercury switch 68 to the thermostatic switch 63 and awire 84 connecting the latter switch to the line conductor 12. It willbe seen that power is supplied to the oil burner through the above described, circuit whenever the switches 26, 68, and 63 are in closedposition. Switches 26 and 68 are normally closed and the burner circuitis complete whenever the switch formed by the thermostatic device 63 isclosed. Switch 26 acts as a safety device breaking the burner circuitwhenever the pilot flame 25 should for some reason become accidentlyextinguished and switch 68 acts as a high limit operating to break theburner circuit whenever the temperature in chamber |'I exceeds apredetermined relatively high value. Thus the switches 26 and 68 shutdown the system in the event of the temperature becoming too high or inthe event of pilot flame failure thereby preventing fuel being forcedinto the combustion chamber when there is no means of igniting the sameand causing consequent danger of explosion.

The circuit for providing electrical energy for operating the dampermotor 5| is formed by a connection from line conductor 12 to terminal 54of the motor, a. wire 8'! which connects to the tion of airin dischargeconduit 31 of the fanhas closed the sailswitch M. In normal operationconsiderable heat is radiated from the economizer 2| which tends to heatthe air in chamber l8 and also to raise the temperature in the pertion3| of chamber ll. When the fan is in operation air is continuallycirculated through the chamber l8 carrying the heat from the economizerinto chamber l1 and preventing the temperature in chamber II from risingunduly high. In conventional arrangements of this type whenever'the fanstops the radiation of heat from the economizer 2| tends to raise thetemperature adjacent the filters 32 to a relatively high value at whichthere is danger of their becoming ignited and causing danger of fire. Inmy arrangement whenever the fan 36 stops for any-reason the switch I isopen and the motor 5| becomes deenergized causing the dampers 45 toclose. Likewise dampers 45 close whenever there is a failure of thesupply of power to motor II. Closure of the dampers isolates the filters32 from the economizer and obstructs the transfer of heat by radiationfrom the economizer to the filters. Positive assurance is thereforeprovided that'the temperature adjacent the filters will not rise to ahigh enough value to cause danger of their becoming ignited.

From the foregoing the operation of the apparatus described should beapparent to those skilled in the art. With the partsin the positionshown the room temperature has fallen to a low enough value so that thethermostatic device 63 has closed the circuit thus calling for heat tobe supplied to the room. The oil burner I! has been started throughthecircuit above described. When the temperature in chamber H has risen toa predetermined value switch 58 closes. Closure of switch 69 causesoperation of the fan 36 and the pressure of the air in the dischargeconduit i'lcauses closure of switch ll. Closure of this switch energizesthe damper motor 5i causing the dampers 45 to be opened. Positivecirculation of the air will now continue until the roomthermostat'becomes satisfied at which time the burner circuit will bebroken. The temperature within chamber I! will then fall to apredetermined value at which switch 89 will open thus deenergizing thefan motor. Upon the fan stopping switch ll will open and damper motor itwill be deenergized permitting thedampers 45 tobe closed by the spring58. It will be seen that at any time during which heat is being suppliedto the rooms should the fan It be stopped due to power failure or thebreaking of the belt or the like, the dampers 45 willbe closedpreventing the temperature adjacent filters I2 rising to an unsafevalue. Should switch 69 fail to close upon a rise in temperature in thechamber II when the room thermostat is calling for heat, the fan'motor31 will not be energized and consequently the dampers .45 M11 not open.It-is apparent therefore that my device insures that at all times thefilters provided L within the furnace casing will be protected fromthereby set fire to the building. The safety features involved eliminatea'very serious fire hazard and the results are accomplished by apositive acting and easily installed device.

Having disclosed one embodiment of my invention it is to be understoodthat this disclosure is to be interpreted as illustrative only and theinvention is to be limited only as determined by the appended claims. I"claim'as my invention:

/ 1. In a warm air heating system, in combination, means for heatingair, means for enforcing circulation of air to and from said heatingmeans, filter means for cleaning the circulating air exposed to heatfrom said heating means and means responsive to failure of the aircirculation enforced by said circulation enforcing means for isolatingsaid filter means from said heating means.

2. In a warm air heating system, in combine-.- tion, means for heatingair, means forcing air to circulate to and from said means, filter meansfor cleaning said air exposed to heat from said heating means, means forisolating said filter means from said heating means, said isolatingmeans being controlled by the forced air circulation provided byvsaidair forcing means so that said filter means becomes isolated from theheating means whenever the forced air circulation ails.

3. In a warm air heating system, in combination, air heating means,means for positively circulating air past said heating means, filtermeans for cleaning. said air exposed to heat from said heating means,means responsive to temperature of air being heated to control said aircirculating means and means controlled in response to the circulation ofair for isolating said filter means from the heating means wheneverpositive air circulation falls.

4. In a warm air heating system, in combination, an air heating means,duct means providing for circulation of air past said air heating means,

, filter means for cleaning air exposed to heat from said heating means,means operable between open and closed posltions'for closing off aircirculation past said heating means and isolating said filter means fromthe heating means, means for enforcing air circulation in said ductmeans and means energized in response to forced air circulation formaintaining said closing means in open position, said energized meansbecoming deenergized whenever forced air circulation fails whereby saidclosing means closes.

5. In a warm air heating system, in combination, a furnace, duct meansfor conveying air to said furnace and a fan for positively circulatinair past said furnace, filter means adjacent saidfurnace and dampermeans between said filter means and said furnace, motor means operablewhen energized to maintain said damper means in open position, meanscomprising a sailswitch responsive to the air circulation controllingsaid motor means so that said motor means is deenergized when the aircirculation does not close said sailswitch. I

6. In a warm air heating system, in combination, a furnace having acasing including a return air chamber, an economizer in said return airchamber and air filter means located adjacent said economizer, dampermeans between said filter means and economizer for isolating the filtermeans from the economizer, means for enforcing responsive to saidenforced air circulation for controllingsaid damper means.

present in a large number 'of heating systems 7. In a warm air heatingsystem, combination, a furnace having a casing, means for circulatingair to be heated through said casing, means providing heat exchangerelation between burnt gases of combustion and air to be heated in saidcasing, filter means for cleaning the air located in said casing andmeans comprising a sailswitch responsive to the air circulation forisolating said filter means from said heat exchange means at apredetermined rate of air circulation whereby the temperature adjacentsaid filter means cannot become excessive.

8. In a warm air heating system, in combination, a furnace, means forcirculating air to be heated to and from said furnace, means formingpart of said furnace for preheating the air circulated to said furnace,filter means for cleaning the air circulated to said furnace, means forshielding said filter means from radiant heat from said preheatingmeans, means comprising a sailswitch responsive to the air circulationcontrolling said shielding means and arranged to cause said shieldingmeans to be moved into shielding position at a predetermined rate of aircirculation whereby the filter means are protected from overheating.

9. In a warm air heating system, in combination, a furnace, meanscomprising a fan for forcing air to be heated past said furnace, saidfurnace having a return air chamber, an economizer comprising a tortuouspassageway for burn gases of combustion located so as to be in heatexchange relation with the return air passing through said chamber, airfilter means located adjacent said economizer, means for obstructingradiant heat fiow between said economizer and said filter means, andmeans comprising a sailswitch and a motor controlled thereby responsiveto the air forced by said fan for moving said obstructing means out ofobstructing position when said sailswitch is closed.

10. In a warm air heating system, in combination, means for heating air,means for circulating air to and from said heating means, filter meansfor cleaning the circulating air exposed to heat from said heatingmeans, and power controlled means operable upon failure of the powersupply for isolating said filter means from said heating means.

11. In a Warm air heating system, in combination, means for heating air,means for circulating air past said heating means, filter means forcleaning said air exposed to heat from said heating means, meansinterposed between said filter means and heating means for isolatingsaid filter means from heat, said interposed means being powercontrolled and assuming isolating position whenever power is notsupplied thereto.

12. In a warm air heating system, in combination, means for heating air,means for circulating air past said heating means, air filter means forcleaning said air exposed to heat from said heating means, and powercontrolled means operable upon failure of power supply thereto toabruptly interpose a heat protective medium between said filter meansand heating means.

13. In a warm air heatingsystem, means for heating air, means forenforcing air circulation past said heating means, filter means forcleaning said air exposed to heat from said heating means, meansinterposed between said filter means and heating means to protect thefilter means from overheating, and control means for said interposedmeans comprising power operated means responsive to failure of theenforced air circulation to cause isolation of said filter means by saidinterposed means, said power operated means also being responsive topower failure for causing isolation of the filter means.

14. In an air heating system, in combination, means for heating air,means for circulating air over said heating means, filter means forcleaning the circulating air exposed to heat from said heating means,said filter means being susceptible to becoming overheated, and meansresponsive to a condition indicating that the said filter means maybecome overheated for isolating said filter means from said heatingmeans.

15. In an air heating system, in combination, air heating means, ductmeans providing for circulation of air past said air heating means,filter means for cleaning air exposed to heat from said heating means,said filter means being susceptible to becoming overheated, meansoperable between open and closed positions for closing off said ductmeans and isolating said filter means from said heating means, means forenforcing air circulation through said duct means, and means responsiveto a condition indicating danger of said filter WILLIAM W. MAR'IENIS.

